But justification for the militants' brutality doesn't stop
with the Quran.

The New York Times
spoke to three ISIS defectors from Raqqa, Syria, who worked
for a female "morality police" brigade before they fled to
Turkey. After they joined ISIS, they were married to fighters,
who provided them with some insight into how the group
defends its violence.

Here's what the women's husbands told them, according to
The Times:

They had to be savage when taking a town to minimize
casualties later, the men insisted. [Syrian President Bashar]
Assad's forces were targeting civilians, sweeping into homes in
the middle of the night and brutalizing men in front of their
wives; the fighters had no choice but to respond with equal
brutality, they said.

This likely isn't surprising to experts, who have said that the
atrocities the Assad regime has committed against Syrians
are the most effective recruiting tool for
ISIS — even better than the slick online propaganda
the group pumps out to lure in foreign fighters and brainwash the
populace it controls.

The strategic security firm
The Soufan Group noted earlier this year that the Assad
regime's brutal treatment of civilians encourages people inside
and outside Syria to support alternate groups that are fighting
for power in the country, including ISIS.

"There is no justifying the actions of a group like the Islamic
State or al-Nusra ... but the Assad regime's wholesale slaughter
of civilians provides the groups with radicalized supporters far
faster than Assad's military can then fight them," The Soufan
Group said.

Assad's atrocities also give power to ISIS's message that it can
protect Syrians from the regime.

Many are also motivated to join ISIS for protection from the
group itself. When ISIS took Raqqa last year, "those who
resisted, or whose family or friends had the wrong connections,
were detained, tortured or killed," according to The Times.

The women who talked to The Times said that they joined ISIS
to survive and "keep life tolerable." Marrying fighters kept
their families in good standing with ISIS. And joining the
morality police — known as the Khansaa Brigade — allowed them
some freedom of movement after ISIS implemented rules that said
women could not leave their homes without a male relative to
escort them.

ISIS also offers a better quality of life for those who join
the group.

"For me, it was about power and money, mostly power," said Asma,
a pseudonym for one of the women who spoke to The Times.
"Since my relatives had all joined, it didn't change a great deal
to join. I just had more authority."